/*
 * Copyright (C) 2010 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.util.concurrent;

import static java.util.logging.Level.SEVERE;

import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.VisibleForTesting;
import java.lang.Thread.UncaughtExceptionHandler;
import java.util.Locale;
import java.util.logging.Logger;

/**
 * Factories for {@link UncaughtExceptionHandler} instances.
 *
 * @author Gregory Kick
 * @since 8.0
 */
@GwtIncompatible
public final class UncaughtExceptionHandlers {
    private UncaughtExceptionHandlers() {}

    /**
     * Returns an exception handler that exits the system. This is particularly useful for the main
     * thread, which may start up other, non-daemon threads, but fail to fully initialize the
     * application successfully.
     *
     * <p>
     * Example usage:
     *
     * <pre>
     * public static void main(String[] args) {
     *   Thread.currentThread().setUncaughtExceptionHandler(UncaughtExceptionHandlers.systemExit());
     *   ...
     * </pre>
     *
     * <p>
     * The returned handler logs any exception at severity {@code SEVERE} and then shuts down the
     * process with an exit status of 1, indicating abnormal termination.
     */
    public static UncaughtExceptionHandler systemExit() {
        return new Exiter(Runtime.getRuntime());
    }

    @VisibleForTesting
    static final class Exiter implements UncaughtExceptionHandler {
        private static final Logger logger = Logger.getLogger(Exiter.class.getName());

        private final Runtime runtime;

        Exiter(Runtime runtime) {
            this.runtime = runtime;
        }

        @Override
        public void uncaughtException(Thread t, Throwable e) {
            try {
                // cannot use FormattingLogger due to a dependency loop
                logger.log(SEVERE, String.format(Locale.ROOT, "Caught an exception in %s.  Shutting down.", t), e);
            } catch (Throwable errorInLogging) {
                // If logging fails, e.g. due to missing memory, at least try to log the
                // message and the cause for the failed logging.
                System.err.println(e.getMessage());
                System.err.println(errorInLogging.getMessage());
            } finally {
                runtime.exit(1);
            }
        }
    }
}
